The present invention relates to methods for testing bond integrity in general and apparatus employing sound waves to detect bond integrity in particular.
In papermaking and many other applications, a rubber or elastomeric coating is bonded to a metal roll, typically a steel roll. In many industrial applications, particular papermaking, a web of material is processed by passing it through a nip formed between a pair of opposed rolls. The width of the contact between the opposed rolls along the direction of motion of the web is referred to as the nip width. Without any compliance, a pair of opposed rolls meets only along a line of contact. Real materials such as steel, which have a high modulus of elasticity, have little or no nip width, and as a result can produce very high pressures within the nip. In many applications a wider nip with a lower pressure is desirable. A wider nip also results in the web passing through the nip having longer dwell time within the nip. Nip dwell time is proportional to nip width and inversely proportional to web speed. A compliant roll cover results in a wider nip. Nip widths of one-half to one inch or more can be achieved with compliant roll covers. Compliant roll covers are typically fabricated of synthetic rubber, or epoxy or other resin system which is sometimes reinforced with fabric.
The rubber, synthetic rubber, or other compliant material must be bonded to a supporting metal roll, typically a steel roll. Bonding is one industrial process in which it is difficult to verify has been properly performed. Careful control of the materials and process used in the bonding is often relied upon to assure quality. However, when new materials or processes are developed, it is highly desirable to be able to non-destructively determine bond integrity. Even with known bonding techniques, unknown variables can result in bonding problems from time to time, creating a need for a technique for detecting the quality of the bond formed between a metal roll and an elastomeric cover.
One known technique for monitoring bonding between an elastomeric cover and the underlying roll, is to tap/strike the bonded roll cover with a wooden stick and listen for changes in the sound produced. With experience a technician can obtain some indication of bond uniformity.
What is needed is an analytical method of detecting the quality of the bond between a roll and an elastic roll cover.